Optical matrix switch with coupler elements

ABSTRACT

An optical matrix switch has N input ports and M output ports and M number of fiber optics coupler elements. One each of the coupler elements is connected to one each of the output ports directly via a fiber optics transmission line. The matrix switch further comprises N×M number of 1×2 fiber optics switch elements with each number 1/N of the total of such 1×2 switch elements connected via a fiber optics transmission line to the input port or to a preceding 1×2 switch element and to one of the coupler elements.

FIELD OF THE INVENTION

The invention relates to an optical matrix switch and, moreparticularly, to an optical matrix switch with switch elements andcoupler elements.

BACKGROUND OF THE INVENTION

Optical matrix switches are useful in optical communication networkswherein large quantities of data are transmitted through optical fibersat high speed. An output optical signal from one of the input opticalfibers, each of which is connected to an optical matrix switch, can besupplied to a selective one of output optical fibers also connected tothe switch.

Optical switching provides certain advantages over electronic switchingtechniques; and, oftentimes, optical matrix switches are utilized inelectronic transmission lines by converting an electrical signal to anoptical signal, passing the signal through the matrix switch andconverting the optical signal back to the electronic signal. Theadvantages of utilizing an optical matrix switch include greatlyincreased band width and rapid switch configuration rates.

Spanke, U.S. Pat. No. 4,787,692, teaches optical switch networks anddesign rules for creating the same. The networks comprise a plurality ofinput and output stages of optical switch elements. Each input opticalswitch stage is comprised of a plurality of 1×2 optical switch elements,and each output stage is comprised of a plurality of 2×1 switchelements. The Spanke patent points out that with its invention utilizingsuch switch network and layout in interconnection, a non-blockingnetwork is achieved having good signal to noise characteristics withoutcrossover and crossthrough limitations as in prior art networks.

Suzuki, U.S. Pat. No. 4,822,124, represents an advancement to the matrixswitch of the Spanke patent. As the Suzuki patent points out, with theconventional optical matrix switch, the size thereof is inevitably largein its longitudinal direction. Thus, for example, where the opticalswitch is provided with four inputs and four outputs to be called a "4×4Optical Matrix Switch", four rows of optical switch elements must beincluded. Therefore, the longitudinal length cannot be less than alength as much as four times the longitudinal dimension of the opticalswitch element. In accord with the Suzuki patent, a stage of 2×3 opticalswitch elements is provided in place of two intermediate stages of 1×2and 2×1 switch elements to thereby result in an optical switch smallerin the longitudinal direction.

Both prior art patents utilize switching elements based on a Ti--LiNbO₃substrate. The interconnection of stages of the input and outputsections includes optical crossovers and crossthroughs diffused in thesame substrate in which the switch elements are formed. The Suzukipatent indicates that, as a result, the substrate on which the four rowsof optical switch elements are provided must be large in surface area,thereby substantially increasing fabric casing costs. With 2×2 groupswitch means in the center stage of s switching matrix, the total numberof switches otherwise required is decreased, and, correspondingly, thetotal number of optical crossover and crossthroughs is decreased. Thus,for example, in Spanke, a 4×4 matrix switch would be constructed using astage 2 consisting of eight 1×2 switches, a stage 1 adjacent to inputports of four 1×2 switches, a stage 3 of eight 2×1 switches, and a stagefour of four 2×1 switches, each connected to an associated output port.With Suzuki, the total of sixteen switches in the intermediate stages 2and 3 would be replaced by a total of four 2×3 switch means, therebyresulting in a matrix switch with a total of twelve switching elements.Again, as with Spanke, the switching elements are Ti--LiNbO₃ substratebased switches.

The present invention takes advantage of certain characteristics offiber optic transmissions that permit the utilization of opticalcombining elements, particularly couplers. Couplers are fiber opticslight transmitting elements for connecting a plurality of transmissionlines and stations. In the present invention, the coupler is a fiberoptics transmitting element that connects a plurality of transmissionlines from fiber optic switch elements and to an output port. Thecouplers uniformly couple an optical signal propagating in any one ofthe plurality of transmission lines from the fiber optics switchelements to a transmission line to the output port. The couplers of thepresent invention are formed from input and output fiber bundles in thefirst instance from a single bundle. To this end a plurality of fibersis first provided. As is known, fibers of one standard configurationcomprise a 50 micron diameter core and a 125 micron diameter claddingsurrounding the core. The fibers are subjected to an etching step or thelike, wherein the cladding, on respective intermediate portions, isreduced to minimal thickness, say 2 microns. Intermediate portions arein the order of two to four inches in length with transmission regionson the order of perhaps one-quarter inch between the full diameter andthe reduced diameter. The etched fibers are then bonded over at leastpart of intermediate portions to provide a rigid assembly. Bonding maybe accomplished by any convenient technique such as fusing or cementing.The fibers are preferably bonded into a parallel closed packagedtriangular or hexagonal configuration. However, no particular symmetryrequirement need be imposed. Bonding permits an incoming signal from anyone of a number of fibers to be transmitted to an output fiber which isfused thereto. The present invention advantageously utilizes couplers ofthis description in a fiber optics matrix switch as hereinafterdescribed.

Further, the present invention takes advantage of advances in the fiberoptics switching art. As pointed out above, both the Spanke and Suzukipatents utilize switching elements based on a Ti--LiNbO₃ substrate. Asboth patents point out, with such switching elements, the longitudinallength of the matrix switch becomes critical. However, advances in thefiber optic switching art make possible the providing of discrete fiberoptic switches which may be combined to form matrix switches wherein thelongitudinal length is not of the criticality of matrix switchesutilizing the substrate switches of the prior art. Switching elementsuseful in the matrix switches of the present invention are those taughtby Gutterman, et al., U.S. Pat. No. 4,854,660, and Kokoshvill, U.S.pending application, Ser. No. 053,220, entitled "Fiber Optic BypassSwitch", filed on May 13, 1987, having European priority No. EP 0 299604 Al. The switch elements of the matrix switches of the presentinvention include an imaging system having a symmetry such as aspherical reflector. The switch also includes a group of optical fiberend faces including a first optical fiber end face via which light istransmitted to the imaging system and at least second and third fiberoptic end faces. A translation mechanism is provided for linearlytranslating the imaging system and the fiber end face group relative toone another between two positions. In a first position, the first andsecond fiber end faces are conjugate with respect to the symmetry of theimaging system so that light from the first fiber is imaged by theimaging system into the second fiber. In a second position, the firstand third fiber end faces are conjugate with respect to the symmetry ofthe imaging system so that light from the first fiber is imaged by theimaging system into the third fiber. Thus, it is possible to switch thelight from the first fiber into the second fiber or into the third fiberdepending on the position of the linear translation mechanism.

SUMMARY OF THE INVENTION

The present invention relates to an optical matrix switch having N inputports and M output ports where N and M each is an integer. The opticalmatrix switch has M number of fiber optics coupler elements. Each of thefiber optic coupler elements is directly connected to one each of theoutput ports. The optical matrix switch comprises N×M number of 1×2fiber optic switch elements. The number of 1/N of the total of such 1×2switch elements is associated with a respective input port. This numberof 1/N of the 1×2 switch elements is arranged longitudinally from theinput port in sequence, with each 1×2 switch element connected to theinput port or to a previous 1×2 switch element and with each of the 1×2switch elements directly connected with at least one of each saidcoupler elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a 4×4 optical matrix switch accordingto Spanke, U.S. Pat. No. 4,787,692.

FIG. 2 is a schematic diagram of a 4×4 optical matrix switch accordingto Suzuki, U.S. Pat. No. 4,822,124.

FIG. 3 illustrates one of the switches useable in the present invention.

FIGS. 4A through 4D each represents a separate bank of a 4 by 4 opticalmatrix switch according to the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a schematic diagram of a 4×4 optical matrix switch accordingto a configuration as defined by the Spanke patent. The optical matrixswitch has four input ports (M), labeled A, B, C, and D and four outputports (N), labeled 1, 2, 3, and 4. Switching stages, which are thelongitudinal number of switches between the input and output ports, aredefined as equal to log₂ 4 +log₂ 4 or to 2+2. Each stage is assigned anumber from 1 to 4 in sequence from the input ports to the output ports.Shown in FIG. 1 are such numbered stages. Further, the stage numberedLog₂ M which is the stage numbered 2, comprises the number 4×4 /2 ofoptical 1×2 switch elements or, in other words, a total of eight switchelements (shown numbered 5 through 12 in stage 2). Each stage betweenthe stage of log₂ M (stage of Log₂ 4=stage 2) and the input portsconsists of one-half of the number of switch elements in the next nearerstage to the stage log₂ M (stage 2). Hence, stage 1 consists of four 1×2optical switches labeled 1 through 4. Further, the stage numbered log₂M+1 (stage numbered 3) consists of M×N/2 (4×4/2=eight) optical 2×1switch elements labeled 13 through 20. As shown, stage 3 has eight 2×1switch elements numbered from 1 to 8. Each stage between the stage log₂M+1 (stage 3) and the output ports comprises one-half of the number of2×1 optical switches. Hence, stage 4 would comprise four of the 2×1optical switches labeled 21 through 24, again as shown in FIG. 1.

With reference to FIG. 2, Suzuki teaches replacing the 1×2 and 2×1switches of stage 2 and stage 3 with four 2×3 switches numbered 5, 6, 7,and 8 in FIG. 2. As shown in a 4×4 configuration, the total switcheswould be 12 and the number of crossovers and crossthroughs is reduced.

FIGS. 4A through 4B each represents a separate bank of a 4×4 opticalmatrix switch according to the present invention. By representation of abank is meant representation of a single and isolated input port withall associated switches, couplers, and output ports. With reference toFIG. 4A, is shown the bank of switches 1, 2, 3, and 4 associated withinput port A and connected to optical couplers 1', 2', 3', and 4'.Coupler 1' couples a signal from input port A as well as signals frominput ports B, C, and D to output port 1. Coupler 2' couples a signalfrom input port A as well as B, C, and D to output port 2. Coupler 3'couples a signal from input port A as well as input ports B, C, and D tooutput port 3. Coupler 4' couples a signal from input port A as well asinput ports B, C, and D to output port 4. Respectively, in FIGS. 4B, 4C,and 4D, are shown banks of switches 5, 6, 7, and 8 associated with inputport B; switches 9, 10, 11, and 12 associated and switches 13, 14, 15,and 16 associated with input port D. As shown, the switches areconfigured longitudinally, one from the other, between an input port anda coupler.

In a 4×4 switch shown, four optical coupler elements 1', 2', 3', and 4'are connected to one each of the four output ports A, B, C, and Ddirectly via a fiber optics transmission line. 4×4 number of 1×2 fiberoptic switch elements complete the optical matrix switch. Each number1/N or 1/4 of the total switch elements (1/4×16=4) is associated with arespective input port, and the same number of the total of such 1×2switch elements is arranged longitudinally from each input port. Each ofthe four 1×2 switch elements is connected via a fiber opticstransmission line to the input port or to a preceding 1×2 switchelement. Each of the four 1×2 switch elements directly communicates, viaa fiber optics transmission line, with at least one of the couplerelements. With reference to FIG. 4A, 1/N or 1/4 of the total switchelements 16 (1/4×16=4 ) is associated with input port A. Four of such1×2 switch elements (in FIG. 4A, numbered 1, 2, 3, and 4) are arrangedlongitudinally from input port A. Each of the four 1×2 switch elements1, 2, 3, and 4 is connected via a fiber optics transmission line to theinput port or to a preceding 1×2 switch element. Each of the four 1×2switch elements (1, 2, 3, and 4) directly communicates, via a fiberoptics transmission line, with at least one of the coupler elements 1',2', 3'and 4', then, via such coupling elements to the output ports 1, 2,3, and 4. Similarly, shown in FIGS. 4B through 4D, are switches 5, 6, 7,and 8 associated with input port B, switches 9, 10, 11, and 12associated with input port C, and switches 13, 14, 15, 4A through 4Dshows couplers 1', 2', 3'and 4' associated with output ports 1, 2, 3,and 4.

With reference to the first and second stages of switches, it is notedthat the matrix switch of the present invention may be turned to an"off" power condition thereby removing power from the system so that nolight signals transmit from any of the input ports to any of the outputports. This capability is provided by the present invention whereby itis not available in the configurations of the Spanke and Suzuki patents.Furthermore, it is notable that both Spanke and Suzuki patents recommendconfigurations longitudinally having a minimum number of stages so as tominimize the number of optical crossovers of optical waveguides whichare taught to be diffused in a substrate. The number of crossovers ofthe present configuration greatly exceed those taught by either Spankeor Suzuki but without the disadvantages of crossover inherent in amatrix comprising waveguides diffused in a substrate. Rather, thepresent switch matrix consists of discrete 1×2 and 2×1 switches inaccord with FIG. 4. Further, with the matrix switch illustrated in FIG.3, light signals and, hence, communications may be made between a singleinput port to a single output port by activation of a minimum number ofswitching elements. Reference is made to FIG. 1 which illustrates inputports as A, B, C, and D and output ports as 1, 2, 3, 4. The entries inthe table indicate the number of switches which need to be powered intoan "on" position in order for a light signal to be transmitted from theindicated input port to the indicated output port.

FIG. 3 schematically illustrates an embodiment of the switch of thepresent invention shown as a 1×2 switch 4 comprising a base 5. Fixedlymounted on the base 5 is a spherical reflector 6. The switch 4 alsoincludes a subassembly 7. The ends 1, 2 and 3 of a group of opticalfibers 8, 9 and 10 are mounted on a movable substrate 11 which formspart of the subassembly 7. The end faces 1, 2 and 3 of the fibers 8, 9and 10 are oriented towards the spherical reflector 6 and are arrangedwith respect to the center of curvature of the spherical reflector 6 sothat the spherical reflector 6 provides optical paths between certainfiber pairs. More particularly, the end faces 1, 2 and 3 are arranged ina group of two and one. The fibers are maintained in position by thesupport structures 12.

The end faces of the fibers may be polished or cleaved. Polished endfaces are provided by a polishing operation to all the fiber ends afterthe fiber ends have been positioned on the substrate 11. The advantageof cleaved end faces is that the fibers may be assembled in preciselydefined positions on the substrate 11.

Screws 13 are mounted in slots 14 and are used for initial alignment ofthe subassembly 7 With respect to the reflector 6. More particularly,when the screws 13 are loosened, the slots 14 serve as guides for thesubassembly 7. Once initial alignment is achieved, i.e. once thesubassembly is positioned for a first switching state, the screws 13 aretightened.

To move the switch from a first switching state to a second switchingstate (i.e. a state in which optical paths are provided betweendifferent pairs of fibers than in the first switching state), a solenoid15 and magnet 16 are used to linearly translate the movable substrate11. The permanent magnet 16 is mounted to the substrate 11.Illustratively, in the first switching state the solenoid 15 is off.When the solenoid 15 is activated by way of connector 17 and lead 18,the magnet 16 is repelled and the subassembly 7 is moved againstadjustable stop 19 so that the second switching state is realized. Theposition of the stop is adjustable by means of screw 20.

While what has been described with reference to FIGS. 3 and 4constitutes a presently preferred embodiment of the invention, it shouldbe recognized that the optical matrix switch may take other forms solong as it consists of the longitudinal arrangement of switches incombination with couplers as defined by the claims. For example,switches of the present invention could very well be configured with anodd number of input ports and/or an odd number of output ports. Notably,both Spanke and Suzuki specify the number of input ports or a number ofoutput ports as being non-zero powers of 2. Hence, neither Spanke norSuzuki could provide a fiber optics matrix switch with an uneven numberof input ports and/or an uneven number of output ports. Accordingly, itshould be understood that the invention is to be limited only insofar asrequired by the scope of the following claims.

I claim:
 1. An optical matrix switch having N input ports and M outputports where N and M each is an integer comprising:M number of fiberoptics coupler elements with one each of said coupler elements connectedto one each of said output ports directly via a fiber opticstransmission line wherein each of said coupler elements comprises agroup of optical fibers bonded into a parallel closed packageconfiguration; N times M number of 1×2 fiber optic switch elements witheach number 1/N of the total of such 1×2 switch elements beingassociated with a respective input port and each of said number 1/N ofthe total of such 1×2 switch elements being arranged longitudinallytherefrom said respective input port with each of said 1×2 switchelements connected via a fiber optics transmission line to the inputport or connected via a fiber optics transmission line to a preceding1×2 switch element and with each of said 1×2 switch elements directlyconnected via a fiber optics transmission line with at least one of eachof said coupler elements.
 2. The optical matrix switch of claim 1 havingN input ports and M equal to N output ports comprising M equal to Nnumber of coupler elements and N² number of 1×2 fiber optic switchelements.
 3. The optical matrix switch of claim 1 having four inputports and four output ports comprising four coupler elements and sixteen1×2 fiber optic switch elements.
 4. The optical matrix switch of claim 1or claim 3 wherein each fiber optic switch element comprises:an imagingsystem having a symmetry; a group of optical fiber end faces including afirst optical fiber end face via which light is transmitted to saidimaging system and a second and third optical fiber end face via whichlight is transmitted away from said imaging system; means for linearlytranslating the group of fiber end faces relative to one another betweena first position and a second position; in said first position, lightfrom said first fiber end face is imaged into said second fiber endface; and in said second position, light from said first fiber end faceis imaged into said third fiber end face.
 5. The switch of claim 4wherein said imaging system is a spherical reflector.
 6. The opticalmatrix switch of claims 1, 3, or 4 wherein said coupler is a fiberoptics transmitting element connecting a plurality of transmission linesfrom said fiber optic switch elements and transmission line to saidoutput port and coupling an optical signal propagating in any one ofsaid plurality of transmission lines from said fiber optic switchelement to said transmission line to said output port.